Field of the Invention
This invention patent relates to a method for reusing expanded bead materials. More particularly, this invention relates to a method for molding expanded polystyrene foam regrind material using a powder adhesive and steam.
Description of the Related Art
Expanded polystyrene (EPS) foam has found popular use as insulation and in packaging materials. EPS beads are produced by injecting pentane (a blowing agent) in tiny polystyrene granules (a.k.a. virgin EPS beads). This process is called primary expansion. The spherical EPS beads are expanded to about 40 times their size by heating polystyrene beads using steam which makes the pentane boil. This process is called secondary expansion. The pentane gas expands under the action of heat, producing a honeycomb-like cell structure. These virgin expanded beads are molded into a three dimensional objects using a machine called steam chest molding machine. During steam chest molding, steam and pressure is applied which causes EPS beads to fuse together. Presence of pentane is extremely critical to the fusion as it is the primary driving force for the fusion. During molding, virgin EPS beads still has less than 2% of pentane trapped in its cell structure. Pentane is a volatile gas under atmospheric conditions and typically EPS beads are molded within 2-3 weeks of secondary expansion. If too much time passes then the beads are “dead” and have no use for the molding. Under heat (steam) and pressure, the pentane gas creates a lot of heat, thus taking the polystyrene above its glass transition temperature of 85 C. Above the glass transition temperature the polystyrene chains are soft and thus bond to create a three dimensional product. A lack of pentane will not raise the temperature beyond 85 C and thus not create any fusion.
Polystyrene is a petroleum-based, non-biodegradable polymer that occupies large volumes of space in landfills and remains there for very long periods of time. Each year large amounts of expanded polystyrene waste are added to landfills across the globe. Due to its adverse environmental impact, some jurisdictions have banned the use of EPS for food packaging.
A method of recycling EPS would help alleviate this problem. Currently, EPS manufacturers are unable to use recycled EPS back in their product since the recycled beads contain no residual pentane. Addition of “dead” EPS beads creates an inferior product with a substantial loss of physical properties.
EPS packaging is used in high quantities to protect big electronic items such as televisions, appliances, printers and other electronic items. These items are fragile and breakage creates recycling problems because electronic items are expensive to recycle. EPS molders are reluctant to reuse recycled EPS since the addition of recycled EPS has a negative impact on the EPS properties.
Thus there is a need for a more efficient system for reusing EPS that would increase the life cycle of each molded bead, increase the amount of recycled EPS that can be used in a molded EPS part, decrease the use of raw materials by the EPS industry and decrease the amount of EPS sent to landfills.
The present invention is designed to meet these needs.